1. Field of the Invention
The present invention relates to a control method for a roller with a built-in motor equipped with an electromagnetic brake used mainly for driving a belt conveyor.
2. Prior Art
In a roller with a built-in motor for a conveyor, an electric brake is normally used to stop the rotation of the roller. In this stopping method, even when the roller rotation stops, the conveyor can still keep on moving because of an external force. In another method, an electromagnetic valve is used to solely stop the rotation of the roller mechanically. However, this method has problems. For instance, the brake pad can easily wear out. In order to avoid this problem, the inventors of the present patent application proposed a method for reducing the friction in Japanese Patent Application No. 339967/1999. In this method, the friction of the friction part is reduced by way of activating an electromagnetic brake after the motor rotation decreases.
Development of high-performance magnets in recent years provides compact and high-torque motors and further small and high-powered rollers with built-in motors. When a small and high-powered roller with a built-in motor is equipped with an electromagnetic brake, there is a problem of insufficient braking force. For example, when stopping a heavily loaded conveyor in an inclined line, it is difficult to maintain the stopped condition. So as to solve this problem, it is necessary to build in an electromagnetic brake having a large stopping power. Such an electromagnetic brake can be achieved by employing a strong brake spring that presses the friction part. To release the brake, however, a high-voltage electric current is needed for the electromagnetic coil to increase the suction force of the electromagnetic coil. This causes another problem. A highly heated electromagnetic coil is required when the brake is released.
Accordingly, the object of the present invention is to provide a control method for a roller with a built-in motor by way of using a strong brake spring and an electromagnetic coil with minimum heat generation, thereby accomplishing a roller with a built-in motor equipped with an electromagnetic brake that has a strong stopping power.
More specifically, the roller with a built-in motor of the present invention is equipped with an electromagnetic brake, wherein a brake spring presses a friction part to activate the brake in a stopped condition, a run signal causes an electromagnetic coil to be energized, and the suction force of the electromagnetic coil cancels the pressure on the friction part in resistance to the resilience of the brake spring; and in order to accomplish the above object, in the present invention, when the motor rotation (rpm) reaches a predetermined value, the electromagnetic coil, which has been energized at a constant voltage by the run signal, is turned off and on repeatedly in a short period of time, thus lowering the average voltage of the electromagnetic coil and reducing the heat generation in the electromagnetic coil.